A conventional caulking gun uses pneumatic power or manual way to drive a press rod into the rear end of a tube of caulking on the caulking gun to let the caulking adhered to the desired position on an object. Generally, the press rod is in contact with the rear end of the tube of caulking no matter whether the pneumatic device is running or not so that when the pneumatic device moves the press rod, the caulking flows from the front end of the tube. Nevertheless, the caulking is a thick and flexible material so that when the pneumatic device stops, the press rod still firmly contacts the rear end of the tube so that the caulking will exert a force on the press rod and a reaction force is applied to the caulking by the press rod to make an extra small amount of the caulking flow from the front end of the tube. Furthermore, when the press rod is pulled back to install a new tube of caulking in the caulking gun, the pneumatic device has to be controlled not to exert a force to the tube of caulking and this action takes time and not efficient.
The present invention intends to provide a caulking gun that has a clutch device to release the press rod from the motor shaft and a planet gear set generates a high torque to the rack.